The proposed study will be conducted with several species of acetogenic bacteria including Clostridium thermoaceticum, Clostridium formicoaceticum, Clostridium thermoautotrophicum and Acetobacterium woodii. These bacteria grow heterotrophically on certain sugars or autotrophically on a hydrogen-carbon dioxide mixture. The product of the metabolism is acetate. The important feature of the acetogenes is their capacity to synthesize acetate from carbon dioxide. The pathway of acetate synthesis includes formate, tetrahydrofolate derivatives and Vitamin B12. The convertion of carbon dioxide to formate is catalyzed by formate dehydrogenase, which contains selenium tungsten and iron. The role of these elements in the catalytic process will be studied using radioactive isotopes and spectrometric methods such as EPR, EXAFS, UV. These studies will increase our understanding on how trace elements function in biological reaction catalyzed by enzymes. Several tetrahydrofolate enzymes have been obtained pure, including formyltetrahydrofolate synthetase, methenyltetrahydrofolate cyclohydrolase, and methylenetetrahydrofolate dehydrogenase. The active sites of these enzymes will be studied and compared using reagents for amino acid modifications and by isolations of active site peptides. These experiments will give knowledge about enzymes converting 1-carbon compounds, which are needed for DNA, RNA and protein synthesis. Work will include isolation of proteins containing derivatives of Vitamin B12. The acetogens when grown autotrophically must produce energy in a process involving the reduction of carbon dioxide. Several electron carriers including cytochrome b, ferredoxins, rubredoxins, and flavodoxins have been isolated from the acetogens. They also contain an ATP-ase. The possible involvement of these carriers in the electron transfer and ATP-generating processes will be studied. It is believed that these processes in the acetogens are primitive and the results would be of importance to interpret the evolution of energy producing biological systems.